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Doesn't ADAT introduce phase shift?
Old 1 week ago
  #1
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Doesn't ADAT introduce phase shift?

I started looking for ADAT extension unit for Scarlett 18i20 and it kinda struck me due to way ADAT slave is configured in 18i20 - doesn't ADAT extension introduce phase shift issues? I mean in scenario where we for example connect left speaker to ADAT master and right one to ADAT slave or something like that. ofc it's a bit exaggerated but I hope my point is clear:

When you connect interface directly path goes like this:
PC -> USB (PCM) -> DA -> speaker

But in case of ADAT slave there's significantly more work:
PC -> USB (PCM) -> DA (optical) -> AD (optical) -> DA -> speaker

considering that in practice optical transceivers usually introduce more latency than electrical ones (at least that's how it works in networking idk if it's the same for audio but copper 10GBASE-T SFP+ transceivers tend to have lower latency than optical 10GBASE-SR ones). I know this delay itself is rather insignificant but my concern is more about creating asymmetric setup where some speakers are connected to master and some to slave and they both coexist in single scene simultaneously. Also probably different devices have itself DACs with different latency of signal conversion and many people create ADAT clusters with various not necessarily the same devices.

Is it what ADAT clock sync is for? So that master "holds" signal a little bit to compensate for ADAT AD/DA transmission delay to slave unit?
Old 1 week ago
  #2
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Quote:
Originally Posted by lapsio View Post
I started looking for ADAT extension unit for Scarlett 18i20 and it kinda struck me due to way ADAT slave is configured in 18i20 - doesn't ADAT extension introduce phase shift issues?
....
Is it what ADAT clock sync is for? So that master "holds" signal a little bit to compensate for ADAT AD/DA transmission delay to slave unit?
A form of this question came up a few weeks ago in another thread. My post is in the link below:
[2 external preamps, one out of phase?

The encode/decode time is not symmetrical in an ADAT device. For example, the ART TubeOpto is 32-samples A/D and 22-samples D/A.

The optical receiver/drivers have negligible effect and there's no store-and-forward happening. Time division multiplexing requires clock reference to establish where the start-of-frame is when there are no addressable packet headers.
Old 1 week ago
  #3
Here for the gear
 

The encode/decode time is not symmetrical in an ADAT device. For example, the ART TubeOpto is 32-samples A/D and 22-samples D/A.

Well that's terrible. Are there better protocols that are buffer size aware and perform corrections to not go out of sync?

I currently ran into scenario where I ran out of outputs and I'm about to obtain ADAT extender. My understanding of your post is that effect of phase desync will be less apparent in case of lower frequencies so if I connect subwoofers to ADAT slave and all speakers to master it shouldn't be too bad right?
Old 1 week ago
  #4
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it's not about phase shift, it's about latency which any piece of digital gear (or plugin introduces) - so no, adat does NOT introduce phase shift! but any two or more signals running through different digital devices are should not get used for for a stereo signal; running say mics on a drumkit through one multichannel preamp and the bass di/cabinet through another is mostly not much if any issue. besides latency can get corrected...
Old 1 week ago
  #5
The original ADAT black face used a Cirrus Logic ADC chip with oversampling. The DAC's were BurrBrown with a passive filter, 10 poles worth. That unit measured 2500 degrees of "group delay" at 20k hz. However, tracks recorded with it were not affected and sound very good played back through a modern top notch DAC.

The ADAT lightpipe digital transfers also sound fine.
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